1. Field of the Invention.
The present invention relates to machines for manufacturing and processing fiber webs, and, more particularly, to a control system used to control physical components of such machines.
2. Description of the related art.
Machines for manufacturing and processing fiber webs can generally be classified as paper machines and off-line coaters. A paper machine receives a prepared fiber suspension and produces a fiber web, such as a paper web. The physical parameters of the fiber suspension which is supplied to the paper machine, such as the pressure, temperature, chemical content, etc. in turn affect the physical characteristics of the fiber web manufactured by the paper machine. It is known to laboratory test a small portion of the fiber web to determine the physical characteristics thereof. After the fiber web is tested, valves, feed screws, pumps or the like may be manually actuated to add a predetermined amount of energy (e.g., heat) or chemical (e.g., calcium carbonate, titanium dioxide, etc.) to the fiber suspension to affect the physical characteristics of the manufactured web. Since this process is manually adjusted, the delay time between obtaining a sample of paper and finally adjusting a device within the approach flow system may be extensive. This means that a relatively large amount of paper may be produced which does not have optimum physical characteristics.
An off-line coater treats a fiber web with one or more coatings to provide desired physical properties to the fiber web, such as brightness, color, surface finish etc. The coater typically receives a large roll of the fiber web, unwinds and coats the fiber web, and rewinds the fiber web after coating.
Regardless whether the fiber web is manufactured using a paper machine or coated using an off-line or on-line coater, the quality of the fiber web must be continually monitored to assure a high quality fiber web as an end product. Certain inherent inefficiencies exist in the manual lab testing techniques commonly employed, as described above.
What is needed in the art is a paper machine which automatically adjusts for at least some of the physical parameters associated with the fiber suspension and/or fiber web to thereby improve the quality of the fiber web.
The present invention provides a chemical process controller which receives input signals from a plurality of sensors spaced along the length of the paper machine, and which controls various control modules of an approach flow system which provides a fiber suspension to a wet end of the paper machine.
The invention comprises, in one form thereof, a paper machine for making a fiber web, including an approach flow system including a plurality of control modules. Each control module controls one of 4 plurality of adjustable input parameters. A wet end receives a fiber suspension from the approach flow system, and includes a headbox which discharges a fiber suspension with a known cross sectional profile onto a wire. A press section, forming section and drying section are used to press, form and dry the fiber web, respectively. A plurality of sensors are respectively positioned in association with the approach flow system, wet end, press section, forming section and/or drying section. Each sensor is configured to sense a physical characteristic of the fiber web and provide an output signal indicative thereof. A chemistry process controller is coupled with each sensor and each control module within the approach flow system to define a closed loop control system. The chemistry process controller controls operation of each control module.
The invention comprises, in yet another form thereof, a machine for one of manufacturing and processing a fiber web. An input end receives a fiber suspension or a fiber web. The input end includes a plurality of control modules, with each control module controlling at least one of a plurality of adjustable input parameters. A plurality of sensors are provided, with each sensor being configured to sense a physical characteristic of one of the fiber suspension and the fiber web and provide an output signal indicative thereof. A chemistry process controller is coupled with each sensor and each control module to define a closed loop control system. The chemistry process controller controls operation of each control module.
An advantage of the present invention is that the physical parameters of the fiber suspension are controlled using a closed loop control system, thereby avoiding the necessity to manually adjust valves, pumps or the like.
A further advantage is that output signals from the sensors may be utilized almost instantaneously to provide a fiber suspension with desired physical parameters to the wet end of the paper machine.